Thermal assessment on tribological properties of turbocharger journal bearing

Abstract

High speed rotation of turbocharger rotor shaft could lead to significant frictional losses generated in journal bearing, which in turn affects the engine minimum speed. Therefore, this study is to mathematically predict the frictional behaviour for a turbocharger journal bearing, considering lubricant film formation and thermal effect. A mathematical model is initially derived from a 2-D Reynolds equation based on finite difference method and Modified Newton Raphson’s Method. Then, a reduced energy equation is integrated, to consider thermal effect. The mathematical model is validated with measured friction power of a typical automotive turbocharger obtained from literature. Through the analysis, it is shown that thermal analysis assumption correlates better with literature experimental data. The significant temperature rise in lubricant leads to the reduction of viscosity as well as the frictional power losses of the turbocharger. A parametric study using Taguchi method is then conducted to optimize parameters, such as bearing width, type of engine oil used as lubricant and bearing radial clearance, for minimizing the friction power loss. The effect of bearing width is found to contribute the most to the frictional power loss, followed by the lubricant oil and lastly, the radial clearance of the bearing.